White goods appliances typically include a low cost interface including one or more mechanical buttons or switches which physically make or break a circuit and one or more rotatable knobs having, typically, a finite number of discrete orientations. Such knobs typically control a potentiometer such that each different orientation causes the potentiometer to present a corresponding resistance to a detector circuit which thereby detects the state of the knob, converts this to a digital value and communicates this to a controlling microprocessor which takes the appropriate action. Alternatively, the knob could be connected to an energy regulator including a bi-metallic strip which bends as it heats or cools to make or break on electrical contact, especially in the case of an electric cooker.
There are a number of problems with such an interface. A physical shaft connects the potentiometer or energy regulator to the outside knob. It is very difficult to seal around such a shaft and so there is usually a risk of contaminants such as water, soap, dirt, etc. gaining access to, and therefore possibly damaging, the potentiometer and the associated electronics. Also, in the case of kitchen equipment, there may be health risks caused by the entrapment of fat or food particles around the shaft. Furthermore, if the knob is to be mounted onto the side of a box in which the potentiometer or energy regulator is mounted, a hole must be preformed (e.g. by drilling) in the correct location on the side of the box for receiving the potentiometer shaft. Similarly, with mechanical push buttons, suitable holes must be preformed through the side of the box where the push buttons are to be mounted. This means that if a manufacturer wishes to produce a similar appliance but with a different arrangement of switches and knobs etc, a new box with different preformed holes must be manufactured, leading to increased manufacturing costs.